Materials such as fabrics are characterized by a wide variety of functional and aesthetic characteristics. Of those characteristics, a particularly important feature is fabric surface feel or "hand." The significance of a favorable hand in a fabric is described and explained in my U.S. Pat. Nos. 4,918,795 issued Apr. 24, 1990 and 4,837,902 issued Jun. 13, 1989 the teachings of which are both incorporated herein by reference.
My previous patents have identified techniques for conditioning textile sheets to change their aesthetic qualities. Specifically, these patents disclose methods and equipment for projecting low pressure, high velocity streams of gaseous fluid against a fabric web in a direction opposite and substantially tangential to the web of fabric, thereby creating saw-tooth waves having small bending radii which travel down the fabric thereby breaking up fiber-to-fiber bonds in the web so as to increase drape and flexibility.
It has been found that some crease-sensitive webs cannot be processed by the technique disclosed and taught in my previous patents without the formation of objectionable longitudinal creases. These creases occur as the web passes from a low tension region before contact with the stream of gaseous fluid to a high tension region after contact with such stream as the frictional interaction of the stream and the web increases the tension of the upstream web.
While the direction of flow of the stream in the previous method is substantially anti-parallel to the direction of travel of the fabric web, it is believed that small variations in flow direction result due to turbulence and discontinuous effects at the edge of the web. Such phenomena are believed to result in waves which have a component thereof which travels in the web direction substantially perpendicular to the direction of web travel which results in a slight narrowing of the web. As the web passes out of the stream of gaseous fluid, the waves are believed to collapse and the web width is substantially recovered, thereby resulting in small creases which may leave permanent marks in the web. This phenomena has been identified as being especially severe in very thin, tightly constructed fabric webs such as those used for computer dot matrix printer ribbons as well as in fabric laminates made up of one or more layers of fabric bonded by a film or adhesive layer or with a film sans fabric.
The common feature among those webs which exhibit undesirable creasing is the existence of relatively high in-plane compression stiffness and relatively low bending stiffness, which results in a reduced ability of the web to accommodate distortions and thereby promote the development of creases as described above. In addition, other materials may occasionally be sensitive to crease marks, especially when run with elevated gas temperatures.
It has been found that, by reversing the direction of web flow relative to the gaseous stream such that they travel in substantially the same direction, and by providing for a relatively low post treatment tension of the fabric web, creasing can be eliminated. This process is most efficient when the web velocity does not exceed approximately 10% of the velocity of the gaseous stream.